The invention concerns a machine of the type for machining a spiral cutting edge on a workpiece having an elongate shank with an at least partially rounded head by relatively moving the workpiece and a rotating machining tool, to produce a machined tool from the workpiece. The machine comprises a support unit having first and second supports mounted for sliding movement relative to one another in a horizontal plane and rotation together about a vertical axis; a headstock carried by the first support, the headstock having a spindle for carrying the workpiece to be machined, and being positionable so that the axis of the spindle intersects said vertical axis; and a device mounted on the second support for helicoidally driving the headstock spindle.
A known machine of this type, described in applicant's U.S. Pat. No. 3,851,563, comprises a carriage carrying a transverse slide on which is mounted a longitudinal slide by means of a support which is rotatable and inclinable on the transverse slide. The device for helicoidally driving the headstock spindle is fixed on the inclinable part of the support and includes a cursor moving along a stationary guide whose angular inclination can be set from 0.degree. to 90.degree. relative to the longitudinal slide. To machine a hemispherical end of a workpiece, the support of the longitudinal slide is inclined by an angle equal to the slope of a spiral to be cut on the cylindrical part of the workpiece, the centre of the sphere is brought onto the vertical axis of rotation, and then, after having brought the rotating machining tool (e.g. a grinding wheel) to the operating position, the support is turned by 90.degree. about the vertical axis. This rotation produces a grinding along a circular arc, i.e. in a plane. Then the device for helicoidally driving the headstock spindle is started, and the ground circular arc is extended by a spiral, with a progressive unbroken joint between the two parts of the machined cutting edge. This machine, which provided a progress over the prior machines since it enabled a continuous machining capable of automation, nevertheless involves some drawbacks. Firstly, the mass that must be held inclined at a very precise inclination is great, and this requires a costly structure. Secondly, although the joint between the extremity of the circular arc (which in projection is rectilinear) and the spiral cutting edge is unbroken, this joint is in the form of an indefinite curve over a relatively short distance. Finally, on its rounded end, the machined tool (for example a spiral cutter) has a non-spiral cutting edge coplanar with the tool axis, and this may adversely effect the machining characteristics of the end of the tool.
An aim of the invention is to obviate these drawbacks.